This invention relates to a fluid-filled vibration damping device, more particularly, to an improvement in the structure of a tubular fluid-filled vibration damping device of the type in which a damping rubber member, in which fluid compartments are formed, is provided between an inner and an outer tube.
A tubular vibration damping device has been proposed as a fluid-filled vibration damping device that can be constructed in a compact form and yet produces a satisfactory damping action to be used advantageously with engine mounts and other vibration sources. Typically, the tubular vibration damping device has a rubber material injection molded within a tubular insert plate to form not only a damping rubber member through which the inner tube extends to be retained thereby, but also, the walls of fluid compartments. The insert plate is then pressed into the outer tube in the working fluid.
An example of this conventional device is shown in FIG. 1. A tubular insert plate 101 has been pressed into an outer tube 104 and has a damping rubber member 102 formed as a molded part in the upper half thereof. An inner tube 103 for supportively coupling a pair of vibrating bodies (i.e., vibration sources) penetrates the rubber member 102 near its bottom wall. The central portion of the rubber member 102 concaves from the periphery of its upper half down to a point close to the inner tube 103, thereby forming a main fluid compartment A between the front and rear sidewalls (as seen in a direction normal to the paper).
The insert plate 101 concaves circumferentially in the central portion and it has openings 111 and 114 formed in its upper and lower halves, respectively (see FIG. 2); opening 111 is in registry with the main fluid compartment A whereas part of the rubber layer that is formed in the concave is stretched across the opening 114 to form a thin rubber wall 123. With the insert plate 101 being pressed into the outer tube 104, a sub-fluid compartment B is formed between the inner surface of the outer tube 104 and the thin rubber wall 123 which defines a wall of compartment B. The sub-fluid compartment communicates with the main fluid compartment A via a flow constricting channel F formed in the rubber layer in the concave. The main fluid compartment A has a stopper member 106 of a substantially, symmetrical shape in cross-section provided in its interior.
If the damping rubber member 102 deforms in response to a vibrational input, the working fluid flows between the main compartment A and the sub-compartment B via the flow constricting channel F, thereby producing a great damping force.
Another example of the tubular fluid vibration damping device that has been proposed to date is shown in FIG. 3. A tubular insert plate 201 has been pressed into an outer tube 204 and has a damping rubber member 202 formed therewith in the upper half thereof. An inner tube 203 for supportively coupling a pair of vibrating bodies is buried through the rubber member 202 near its bottom wall. The central portion of the rubber member 202 concaves from the periphery of its upper half down to a point close to the inner tube 203, thereby forming a main fluid compartment A between the front and rear sidewalls (as seen in a direction normal to the paper).
The insert plate 201 concaves in the central portion of the entire circumference and an annular constricting member 271 is positioned in the concave. The insert plate 201 has a larger concave in its lower half and the periphery of a thin rubber wall 272 is held between the outer tube 204 and the edge of an opening in the constricting member 271, thereby forming a sub-fluid compartment B above the rubber wall and an air compartment D therebelow.
The main fluid compartment A and the sub-fluid compartment B can communicate with each other via a flow constricting channel F formed in the constricting member 271. The main fluid compartment A has a stopper member 273 of a substantially symmetrical cross-section provided in its interior. The damping rubber member 202 through which the inner tube 203 extends has a cushioning rubber plate 274 positioned below the bottom wall thereof.
If the damping rubber member 202 deforms in response to a vibrational input, the working fluid flows between the main compartment A and the sub-compartment B via the flow constricting channel F, thereby producing a great damping force.
Each of the two examples of the above described conventional tubular vibration damping device have deficiencies. In the first example of FIG. 1, the thin rubber wall 123 faces the inner tube 103 directly, although there is a certain clearance therebetween. If the inner tube 103 is displaced greatly downwardly by the vibrational input, it may potentially interfere with the thin rubber wall 123 and experience wear fatigue. Additionally, any excessive downward displacement of the inner tube 103 cannot be restricted effectively and the resulting excessive stress on the damping rubber member 102 can potentially reduce its durability.
In the second example of FIG. 3, the thin rubber wall 272 is formed as a separate part from the damping rubber member 202 and, after it is held between the constricting member 271 and the outer tube 204 in the working fluid, part of the fluid which has been trapped in the air compartment D is withdrawn through a pair of holes 241 and 242 that are formed in the sidewall of the outer tube 204 on the right and left sides. Thus, the manufacture of the second example of fluid-filled vibration damping device involves extra steps such as the storage and mounting of the thin rubber wall 272 and water draining, which adds to the overall production cost of the device.